Two of my indoor cats escaped through a window screen this past weekend (my one cat rips the screens and then goes out - he comes back in through the same screen that's now ripped). Anyway, one came back and one didn't. Neither one had collars nor are they micro-chipped. I decided that if I ever found the missing cat that I would get them both collared and chipped. I don't trust collars though. I remembered that years ago I had a cat that I had to feed through it's stomach with a feeding tube. The vet had me buy a small harness (to fit the cat) and on the back/neck of the harness is the ring where you can attach the leash. Well, that is where the feeding tube was secured - from his stomach through the ring at which there was a device that closed and opened the feeding tube for feeding also preventing the tube from falling out of the ring. He loved it! anyway, why not use a harness and attach the ID tags to that ring rather than a collar! the harness is much more likely NOT to come off and it does not restrict their neck. Also, you would be prepared to attach a leash and take the cat out for a walk if you wanted! By the way, the missing cat DID show up in my neighbors yard meowing when I called his name. I have now talked myself into finding harnesses to fit the cats - which I will keep on them at all times providing of course that they will tolerate them. If not, then I will definitely micro-chip the cats at least.